In the process of manufacturing semiconductor devices, photolithography techniques are used for forming circuit patterns on semiconductor wafers (which will be simply referred to as “wafers”, hereinafter), which are treated as target substrates. Where a circuit pattern is formed by use of photolithography, the process steps are performed, as follows. Specifically, a resist liquid is first applied to a wafer to form a resist film. Then, the resist film is irradiated with light to perform light exposure on the resist film in accordance with the circuit pattern. Then, the resist film is subjected to a developing process.
In recent years, the integration degree of semiconductor devices becomes increasingly higher to improve the operation speed and so forth. Accordingly, photolithography techniques are required to increase the miniaturization level of circuit patterns formed on wafers. As a photolithography technique for realizing a high resolution of a 45-nm node level, there has been proposed the following immersion light exposure (for example, see International Publication No. WO 2005/029559). In this immersion light exposure, a light exposure liquid, such as purified water, having a refractive index higher than air is supplied between the wafer and light exposure projection lens. The wavelength of light radiated from the projection lens is shortened by means of the refractive index of the light exposure liquid, so that the line width obtained by the light exposure is decreased. However, the immersion light exposure process brings about several problems in realizing a high resolution of a 45-nm node level where it is utilized alone. Accordingly, studies have been made to combine it with a double patterning technique arranged to perform patterning twice to form a fine pattern.
In the double patterning technique, light exposure needs to be performed twice before etching, so particles generated before the light exposure can be easily carried into the light exposure apparatus. Further, in the immersion light exposure, a light exposure process is performed while a light exposure liquid, such as purified water, is supplied, and so particles can be easily generated in the light exposure apparatus. If particles are present in the immersion light exposure, the immersion light exposure apparatus may be contaminated and thereby deteriorate the light exposure accuracy.
Such particles are generated particularly when defects, such as film peeling, are caused at the wafer edge portion during a process step after formation of a coating film, such as a resist film. Particles generated due to defects at the wafer edge portion contaminate the immersion light exposure apparatus and can not only deteriorate the light exposure accuracy but also copy defects on the front and back sides of wafers.